This invention relates to a structure for miniaturizing a wrist of an industrial robot.
FIG. 7 is a schematic diagram of a conventional industrial robot. This industrial robot generally makes motions similar to ones of portions of a human body from the shoulder to the wrist.
In FIG. 7, a shoulder 2 is provided rotatably on a base 1. An upper arm 3 is mounted swingably on the free end portion of this shoulder. A forearm 4 is provided at the free end portion of the upper arm 3 so that the forearm 4 can swing with respect to the upper arm 3. The forearm 4 is driven via a forearm driving motor (no shown), a lever 47 and a driving link 48. A wrist base 5 is provided on a front portion of the forearm 4 so that the wrist base 5 can rotate around the longitudinal axis of the forearm 4. A wrist body 6 is provided on a front portion of the wrist base 5 so that the wrist body 6 can swing around a pivot extending at right angles to the axis around which the wrist base 5 rotates. A wrist tip 7 is provided on a front portion of the wrist body 6 so that the wrist tip 7 can be rotated around an axis extending at right angles to the wrist body-swinging pivot. Various kinds of instruments 8, such as a tool, a welding torch or a handling device are attached to the wrist tip to carry out various machining and processing operations. The above description is of the construction of a commonly used wrist of an industrial robot. There is also a wrist of an industrial robot, the construction of which is partially different from that of the abovementioned industrial robot wrist. For example, the wrist base-rotating axis, wrist body-swinging axis and wrist tip-rotating axis referred to in the above statement extend at substantially right angles. The angles of these axis do not necessarily cross each other at right angles and they can be regulated in accordance with the working posture.
Japanese Patent Laid-Open No. 59390/1984 discloses a construction of a conventional industrial robot wrist, as discussed above. According to the technique disclosed in this publication, motors for rotating a wrist tip and swinging a wrist body and reduction gears are provided within a wrist base so that this wrist can also be applied to a small-sized industrial robot.
According to the prior art disclosed in the above publication, however, the two motors in the wrist base are parallel-arranged so that each of them orients at right angles to the lengthwise axis of the wrist. Therefore, it is difficult to miniaturize a wrist which generally has an elongated structure of a columnar shape.
If these two motors are arranged so that they extend in the lengthwise direction of the wrist, the following problems which must be solved arise. (1) The transmitting of a driving force from a motor to a tip portion of the wrist is generally done by a belt (including a chain), which is generally extended in the lengthwise direction of the wrist in view of the necessity of miniaturizing the wrist. If these motors are arranged in this manner, it becomes necessary that the driving force from the lengthwise-arranged motors be transmitted to the belts after the direction of the driving force has been changed at right angles, so that the length of the driving force transmitting path increases. If the driving force transmitting path increases, the path along which an external force imparted to the tool at the free end of the wrist tip is transmitted also increases. This would cause the wrist to be displaced accordingly with ease, i.e., the rigidity thereof decreases. (2) If the two motors are arranged in the lengthwise direction of the wrist with no sufficient space left between the rear ends of the two motors and structural members of the wrist facing the rear ends, it becomes troublesome to take out the motors when the maintenance work for the wrist is carried out. Since the output shaft of a motor is generally meshed with a gear, the motor must be taken out by moving the motor in the axial direction thereof. However, when the length of the wrist is not set so large, the motor cannot be moved axially. In such a case, it is necessary that the motor be taken out by moving it in a direction perpendicular to the lengthwise axis thereof. This makes it necessary to disassemble the gear box meshed with the output shaft of this motor, so that the motor-removing operation becomes troublesome. Summary of the Invention
An object of the present invention is to provide an industrial robot capable of being miniaturized by arranging a wrist tip-rotating motor and a wrist body-swinging motor in the lengthwise direction of the wrist, preventing a decrease in the rigidity of the wrist, and carrying out the maintenance work therefor with ease.
A wrist mechanism of an industrial robot according to the invention comprises a forearm, a wrist base provided rotatably around a lengthwise axis of the forearm, a wrist body provided swingably around a pivot or shaft (swing shaft) disposed perpendicularly to the lengthwise axis of the wrist base, a wrist tip portion provided rotatably around a rotary shaft perpendicular to the swing shaft around which the wrist body is swung, and the wrist base has a motor for rotating the rotary shaft and a motor for driving the swing shaft to cause the wrist body to swing around the swing shaft, those two motors being arranged opposite to each other in a lengthwise direction thereof.